The present invention relates generally to an exposure method and an apparatus that exposes a pattern of a reticle (mask) onto a plate to be exposed, such as a wafer, and, more particularly, to a detection of a surface form of the reticle. The present invention is suitable, for example, for a scanning type projection exposure apparatus that synchronously scans the reticle and the wafer to a projection optical system.
The photolithography technology for manufacturing fine semiconductor devices, such as semiconductor memory and logic circuits, has conventionally employed a reduction projection exposure apparatus that uses a projection optical system to project and transfer a reticle pattern onto a plate to be exposed. A numerical aperture (NA) of the projection optical system has recently increased. As a result, a focal depth has been further reduced. Then, an imaging error (a defocus or a distortion error) cannot be disregarded, and it is necessary to detect a surface form (a surface position or a deformation) of the reticle and to correct focus based on a detection result. Especially, an exposure apparatus in a step-and-scan manner (hereafter, “a scanner”) that exposes the reticle pattern onto the plate, while synchronously scanning the reticle and the plate, needs a focus correction during scanning exposure.
It is necessary to measure the surface form of the reticle actually mounted in the exposure apparatus to correctly measure a deformation amount of the reticle. Therefore, a conventional detecting system irradiates a detection light to a pattern surface of the reticle (a grazing incidence method), receives reflected light from the pattern surface, and measures the surface form of the reticle. The detecting system measures the surface form of the reticle at a predetermined timing (for example, a predetermined time interval, one or plural shots, wafer or lot).
As conventional technology, for example, there are Japanese Patent Application, Publication No. 6-36987, Japanese Patent Application, Publication No. 10-214780, Japanese Patent Application, Publication No. 11-26345, and Japanese Patent Application, Publication No. 2003-264136. Moreover, as conventional technology, for example, there are Japanese Patent Application, Publication No. 2003-297726, Japanese Patent Application, Publication No. 2005-085991, and Japanese Patent Application, Publication No. 2003-273008.
However, an influence of the reticle pattern cannot be disregarded according to a demand of further increasing precision for the detecting system. For example, when the reticle is made of a glass substrate and the pattern is formed by chromium, a reflectivity in a pattern area (chromium) for the detection light is different from a reflectivity in a non-pattern area (glass substrate) for the detection light. When the detection light is irradiated, a boundary between the pattern area and the non-pattern area, as shown in FIG. 4B, a waveform of the reflected light changes and shifts from a Gaussian distribution as shown in FIG. 4A. As a result, a center of gravity position shifts from the original boundary (error measurement), a correct surface form of the reticle is undetectable, and transfer performance deteriorates.
It is difficult to increase the number of measurement points in a scanning direction, maintaining a scan speed and a processing speed of a measurement result. On the other hand, if the scan speed and the processing speed of a measurement result are delayed, and the number of measurement points in the scanning direction is increased, throughput decreases. If the reticle is moved in the scanning direction at a specific pitch and a still measurement is executed to the entire reticle pattern in the position, the error measurement position is manifested. However, this method causes the decrease of throughput similarly.